The majority of P-450 genes are regulated at the transcriptional level. During distinct stages of development, P-450 genes became transcriptionally activated. We are studying several of these P- 450 genes that are activated during development. The genes have been cloned and completely sequenced and their promoter regions have been identified. The genes being examined are IIAI, IIA2, IIC7, and IIEI. IIAI and IIEI became transcriptionally activated immediately after birth in both males and females. IIAI, however, becomes specifically suppressed in males at puberty. IIA2 becomes activated in males when they reach puberty and is never expressed in females. IIC7 is activated in both males and females at puberty. To study the cis- and trans-acting elements responsible for these gene activations, we are using a cell-free in vitro transcription system derived from rat liver. Promotor regions of each of the above genes were faithfully transcribed in the cell- free system. Efforts are under way to characterize DNA sequence elements and protein factors responsible for activating transcription of these genes.